The present invention relates generally to systems for providing fresh air to aircraft when parked at a location on the ground. More particularly, the invention relates to a system that can adaptively regulate its operation during periods of considerable thermal load to maintain operation at a reduced level rather than interrupting operation completely.
Various air conditioning systems have been developed for providing conditioned air to aircraft. During flight, power plants (engines) used to drive the aircraft also generate power that can drive on-board conditioned air circulation systems. When parked on the ground, however, conditioned air may be supplied by external means. Air conditioning or refrigeration units may be provided adjacent to such aircraft and coupled to the aircraft by air conduits. Such refrigeration systems, may be either electrically powered or engine-driven. The thermal load encountered by the refrigeration systems, however, can vary greatly, depending upon the part of the world in which the aircraft is operating, the season and environmental temperatures, the size of the aircraft, and the air temperature and flow rates demanded of the refrigeration systems.
A drawback of conventional aircraft conditioned air supply systems, particularly of refrigeration systems, is their reaction to variable thermal loads caused by high or low ambient conditions. Single or multiple refrigeration systems have been provided to allow for reacting to increased loads, and various flow rates, while still maintaining a desired air temperature. However, when external temperatures rise significantly, adding to the thermal load on the refrigeration units, excessive refrigerant pressures may be encountered that force the units to shut down, significantly reducing or interrupting the flow of conditioned air to the aircraft. While the flow of air may be maintained by blowers, the temperature within the aircraft may significantly increase due to the interrupted operation of one or more of the refrigeration system.
There is a need, therefore, for improved approaches to providing conditioned air to parked aircraft. There is a particular need for approaches that will allow continued operation, even if at less than optimal temperatures or flow rates, but that will avoid the shut down of one or more refrigeration units completely.